Originally posted 3 Jan 2009:
I have a long thread, with lots of pictures of the aerodynamic mods that I have done to my Scion xA, over at EcoModder.com
The grill block and the fog light covers were the best improvements = +10% or so improvement in overall fuel economy.
The smooth wheel covers helped ~6% or so.
The rear wheel skirts, and the Kamm back helped some, too.
I'm still keeping above 41mpg even during the winter cold and ice and snow. Before I started ecodriving, my best MPG on a tankful was 42.5, so getting just shy of this for my worst tankful during a New England winter, is a good thing; if I say so myself!